The present invention relates to power supplies in general and more particularly to power supplies incorporating feedback circuits to regulate DC output voltage.
Many prior art power supplies, particularly high voltage power supplies, have used an oscillator to produce a sinusoidal AC voltage of a desired amplitude which is then rectified and filtered to produce a DC output. To improve the regulation of such power supplies, the DC output voltage is sampled and used in a feedback arrangement to control the peak voltage of the oscillator. A drop in DC output voltage due, for instance, to an increase in power supply load causes a corresponding increase in oscillator peak voltage. The increase in oscillator peak voltage then results in an increase in DC output voltage to compensate for the original drop. Likewise, a decrease in power supply DC output voltage would cause an increase in oscillator peak voltage and a subsequent compensating increase in DC output voltage.
Unfortunately, in many applications the response of the oscillator driven power supply to a change in feedback control voltage is too slow to regulate for high frequency output voltage transients. Since the DC output voltage of such a power supply is a function of the peak voltage of the oscillator, it may take as much as one cycle of the oscillator output signal before the change in applied oscillator peak voltage is perceived by the rectifying and filtering circuits. Further, once a change in oscillator peak voltage occurs, capacitors in the filtering circuits of the power supply require additional time to charge or discharge to the desired DC output voltage level. Depending on the relative size of the capacitors and the load impedance, the capacitor charge or discharge time can be considerable.
Therefore what is needed is a regulated power supply capable of fast and accurate compensating response to a small transient change in DC output voltage while also being capable of compensating for wide swings in output voltage due to load changes.